Organic electronic devices and circuits, such as, organic photovoltaics (OPV), organic light emitting diodes (OLED), organic electrophoretic displays, organic electrochromic displays, and the like, are becoming increasingly prevalent in social and commercial uses. OLED, for example, have utility in virtual-view and direct-view displays, as lap-top computers, televisions, digital watches, telephones, pagers, cellular telephones, calculators, large-area devices.
Various package geometries are known for organic electronic devices and circuits, and in general, these geometries consist of an active organic component disposed between a substrate/backsheet (hereinafter interchangeably used) and a cover/frontsheet (hereinafter interchangeably used), and the substrate and cover are adhered together with a laminating adhesive or an encapsulant that encloses the active organic component. One or both of the substrate and the cover are made of a transparent material, for example, transparent glass and flexible thin plastic films. The active organic component is attached to the substrate, and in some embodiments, is covered with an inorganic barrier coating, a buffer film or a coating composed of an inorganic and/or organic layer that seals the contact area between the component and the substrate at its perimeter. An encapsulant is applied over the active organic component, and over the barrier coating, when present. This encapsulant fills the space between the substrate and the cover, encloses the active organic component and adheres the substrate to the cover. In some embodiments, a desiccant package, in the form of a pouch, or a thin or thick film, is attached to the cover, usually in an indentation or cavity in the cover, or alternatively, the desiccant is provided in grooves within the cover.
Most active organic components within organic electronic devices are susceptible to degradation by moisture and oxygen. For example, an OLED, simply described, consists of an anode, a light emitting layer, and a cathode. A layer of a low work function metal is typically utilized as the cathode to ensure efficient electron injection and low operating voltages. Low work function metals are chemically reactive with oxygen and moisture, and such reactions will limit the lifetime of the devices. Oxygen and moisture will also react with the light emitting organic materials and inhibit light emission. Therefore, the packages surrounding the active organic components are designed to restrict transmission of both oxygen and water vapor from the environment to the active organic components.
An encapsulant with pressure sensitive adhesive properties can be used to restrict transmission of oxygen and water vapors, and the pressure sensitive adhesive is typically provided in a thin film between two silicone release carrier films (liners) as an encapsulant film. Upon removal of one of the liners, the exposed encapsulant film is attached to either the cover or the substrate of the device. Subsequently, the second liner is removed, allowing the cover and the substrate to be laminated (or attached) to one another. The encapsulant film must maintain adhesion and flexibility upon long term exposure to strain.
An encapsulant film or encapsulant (hereinafter interchangeably used) with pressure sensitive adhesive properties can facilitate manufacturing through-put of the device. While manufacturing speed and toxicity are improved for encapsulant with pressure sensitive adhesive properties, drawbacks include poor wet out and void formation during assembly because films typically have higher viscosity than their liquid encapsulant counterparts at assembly temperatures. This problem is exacerbated for substrate that contains components such as, electrodes, bus bars, ink steps, integrated circuits, wires, and the like, due to their irregular surfaces. In order to obtain better wet out and to minimize the formation of voids, hot lamination is usually applied to the uncured encapsulant film. However, organic components are sensitive to heat and prolonged exposure to heat is detrimental to the components. Also, because the encapsulants are pressure sensitive adhesive film, the film must maintain minimal cold flow at room temperature during prolonged storage.
WO 2009/148722 and WO 2011/062932 disclose the use of high (typically greater than 300,000 Da) weight average molecular weight (Mw) polyisobutylene-based encapsulants. Such encapsulants yield pressure sensitive adhesive films having high viscosity, and thus are susceptible to voids or air bubbles in organic electronic devices. While application temperature can be increased to minimize this problem, active organic components start to decompose at about 120° C. Moreover, encapsulants made from such high Mw are formed by solution casting, and are not extruded as hot melts, unless extreme temperatures and pressure can be utilized.
JP2012057065 discloses non-curable encapsulants with pressure sensitive adhesive properties. In order to properly wet the substrates with components and to minimize void formations, the viscosity of the encapsulant film must be kept below 1,000,000 cps or below 200,000 Da viscosity average molecular weight (Mv) at 120° C. Furthermore, the thermal plastic encapsulant exhibits cold flow under strain during the lifetime of the device.
Therefore, there is a need in the art for a curable encapsulant film that can laminate at temperatures below 120° C., maintain good adhesion, wet-out on the substrates with irregular surface, minimize cold flow, and form a void-free encapsulation while allowing for flexibility of the substrates over long term exposure to strain. The current invention fulfills this need.